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how to count row and column of a matrix

MathWorks Answers Support. Open Mobile Search. Trial software. You are now following this question You will see updates in your activity feed. You may receive emails, depending on your notification preferences. Vote 0. Edited: Kawsar Ahmed Asif on 13 Dec Accepted Answer: the cyclist.

Accepted Answer. Vote 5. Cancel Copy to Clipboard. Muhammad nasiri on 14 NovDocumentation Help Center. Create a table with four variables listing patient information for five people. If A is a table, numel returns the number of elements in the table, Aequivalent to prod size A. Variables in a table can have multiple columns, but numel A only accounts for the number of rows and number of variables. If A is a character vector of type charthen numel returns the number of characters.

However, if A is a string scalar, numel returns 1 because it is a single element of a string array. This function fully supports tall arrays.

For more information, see Tall Arrays. This function fully supports GPU arrays. This function fully supports distributed arrays. A modified version of this example exists on your system.

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mxGetN (C and Fortran)

Select the China site in Chinese or English for best site performance. Other MathWorks country sites are not optimized for visits from your location. Toggle Main Navigation. Search Support Support MathWorks. Search MathWorks. Off-Canvas Navigation Menu Toggle. Examples collapse all Number of Elements in 3-D Matrix. Open Live Script. String Array. Number of Elements in Cell Array. Number of Elements in Table.

Input Arguments collapse all A — Input array scalar vector matrix multidimensional array table timetable. Input array, specified as a scalar, vector, matrix, multidimensional array, table, or timetable. Tips If A is a table, numel returns the number of elements in the table, Aequivalent to prod size A.

Extended Capabilities Tall Arrays Calculate with arrays that have more rows than fit in memory.Indexing into a matrix is a means of selecting a subset of elements from the matrix. Indexing is a key to the effectiveness of MATLAB at capturing matrix-oriented ideas in understandable computer programs. Vectorization means using MATLAB language constructs to eliminate program loops, usually resulting in programs that run faster and are more readable. Of the many possible vectorization techniques, many rely on MATLAB indexing methods, five of which are described in this article.

The special end operator is an easy shorthand way to refer to the last element of v:. Combine the colon operator and end to achieve a variety of effects, such as extracting every k-th element or flipping the entire vector:.

count rows in matrix ?

By using an indexing expression on the left side of the equal sign, you can replace certain elements of the vector:. Usually the number of elements on the right must be the same as the number of elements referred to by the indexing expression on the left. You can always, however, use a scalar on the right side:. Most often, indexing in matrices is done using two subscripts—one for the rows and one for the columns.

The simplest form just picks out a single element:. A single : in a subscript position is shorthand notation for 1:end and is often used to select entire rows or columns:.

There is often confusion over how to select scattered elements from a matrix. For example, suppose you want to extract the 2,13,2and 4,4 elements from A. The expression A [2 3 4], [1 2 4] won't do what you want. This diagram illustrates how two-subscript indexing works:.

Extracting scattered elements from a matrix requires a different style of indexing, and that brings us to our next topic. When you index into the matrix A using only one subscript, MATLAB treats A as if its elements were strung out in a long column vector, by going down the columns consecutively, as in:. The expression A 14 simply extracts the 14th element of the implicit column vector.

Indexing into a matrix with a single subscript in this way is often called linear indexing. Consider again the problem of extracting just the 2,13,2and 4,4 elements of A. You can use linear indexing to extract those elements:. That's easy to see for this example, but how do you compute linear indices in general? MATLAB provides a function called sub2ind that converts from row and column subscripts to linear indices.

You can use it to extract the desired elements this way:. But what if k is a function of the row number? That is, what if k is a vector of length m?

number of columns in matrix matlab

Is there a quick and easy way to do this?Sign in to comment. Sign in to answer this question. Unable to complete the action because of changes made to the page. Reload the page to see its updated state. Choose a web site to get translated content where available and see local events and offers. Based on your location, we recommend that you select:. Select the China site in Chinese or English for best site performance.

Other MathWorks country sites are not optimized for visits from your location. Toggle Main Navigation. Search Answers Clear Filters. Answers Support MathWorks. Search Support Clear Filters. Support Answers MathWorks. Search MathWorks. MathWorks Answers Support. Open Mobile Search. Trial software.

You are now following this question You will see updates in your activity feed. You may receive emails, depending on your notification preferences. Rakesh Praveen on 7 Nov Vote 5. Answered: Thulitha Theekshana on 17 Jul Accepted Answer: Oleg Komarov.

Anand Gehlot on 16 Oct Cancel Copy to Clipboard. Use height T. Image Analyst on 16 Oct If for example your matrix is A, you can use : size A,1 for number of rows. Also there are some other ways like : length A :,1 for number of rows. Accepted Answer. Oleg Komarov on 7 Nov Vote Hoang-Linh To on 19 May Thank you so much, that's also what I want :.Documentation Help Center.

Call mxGetN to determine the number of columns in the specified mxArray. If the specified mxArray has more than two dimensions, then call mxGetDimensions to find out how many elements are in each dimension. If pm points to a sparse mxArraymxGetN still returns the number of columns, not the number of occupied columns.

number of columns in matrix matlab

The value returned by this function, however, is not a pointer. Choose a web site to get translated content where available and see local events and offers. Based on your location, we recommend that you select:.

Select the China site in Chinese or English for best site performance. Other MathWorks country sites are not optimized for visits from your location. Toggle Main Navigation. Search Support Support MathWorks. Search MathWorks. Off-Canvas Navigation Menu Toggle. C Syntax include "matrix. Fortran Syntax include "fintrf. Arguments pm Pointer to an mxArray. Returns Number of columns in the mxArray. Description Call mxGetN to determine the number of columns in the specified mxArray. Select a Web Site Choose a web site to get translated content where available and see local events and offers.

Select web site.Documentation Help Center. These approaches are indexing by position, linear indexing, and logical indexing. The most common way is to explicitly specify the indices of the elements. For example, to access a single element of a matrix, specify the row number followed by the column number of the element. You can also reference multiple elements at a time by specifying their indices in a vector.

For example, access the first and third elements of the second row of A. To access elements in a range of rows or columns, use the colon. For example, access the elements in the first through third row and the second through fourth column of A.

An alternative way to compute r is to use the keyword end to specify the second column through the last column. This approach lets you specify the last column without knowing exactly how many columns are in A. If you want to access all of the rows or columns, use the colon operator by itself. For example, return the entire third column of A. For example, directly access a column of a datetime array. For higher-dimensional arrays, expand the syntax to match the array dimensions. Consider a random 3-byby-3 numeric array.

Access the element in the second row, third column, and first sheet of the array. For more information on working with multidimensional arrays, see Multidimensional Arrays. Another method for accessing elements of an array is to use only a single index, regardless of the size or dimensions of the array.

This method is known as linear indexing. While MATLAB displays arrays according to their defined sizes and shapes, they are actually stored in memory as a single column of elements.

A good way to visualize this concept is with a matrix. While the following array is displayed as a 3-by-3 matrix, MATLAB stores it as a single column made up of the columns of A appended one after the other. The stored vector contains the sequence of elements 124533362925914811and can be displayed using a single colon.

For example, the 3,2 element of A is 25and you can access it using the syntax A 3,2.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time.

number of columns in matrix matlab

Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Use the size function. The second argument specifies the dimension of which number of elements are required which will be '2' if you want the number of columns. It might appear as a small saving, but size. When want to get row size with size function, below code can be used:. Learn more. How to get the number of columns in a matrix? Ask Question. Asked 8 years, 5 months ago. Active 5 years, 1 month ago.

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Import from Excel and Plot in MATLAB - Sylvia Clay

Scottie T Scottie T 9, 9 9 gold badges 40 40 silver badges 58 58 bronze badges. I think it is generally a good practice to avoid using length on matrices and use size instead. Scottie what does 2 stand for?

MATLAB - Matrix

Evgeni Sergeev Evgeni Sergeev 16k 14 14 gold badges 87 87 silver badges 98 98 bronze badges. Mustafa Kemal Mustafa Kemal 11 11 silver badges 19 19 bronze badges. As a noob to Octave, thank you for writing this out in a way that makes it easy to read. Sign up or log in Sign up using Google.


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